a. Field of the Invention
This invention relates to an NC data creation method for automatically creating NC data for wire-cut electrical discharge machining.
b. Description of the Related Art
In wire-cut electrical discharge machining, a blank is formed with a machining starting hole in advance, and a wire is stretched so as to be capable of passing through the hole and paid out. The blank is adapted so as to be capable of being moved relative to the wire. An electrical discharge is produced by applying a high voltage across the wire and the blank while the aforementioned relative movement is taking place, and the blank is machined by the energy of the electrical discharge.
In creating the NC data for such wire-cut electrical discharge machining, the machining starting point of a part profile, the part profile data (path data) and the machining end point must be specified in addition to various auxiliary information (approach method, withdrawal method, wire severing method, etc.).
To accomplish this, the conventional practice is to directly enter, by means of a keyboard or the like, the coordinates of the machining starting point, the coordinates of the machining end point, and path data including the type of path (straight line or circular arc) and path end point in each path block.
Although the machining starting point and the part profile (path data) can be readily grasped from a design drawing of the part, the machining end point cannot be determined from the design drawing. Accordingly, each machining end point is manually computed, the coordinates thereof found and then entered.
As shown in FIG. 10, a machining end point M.sub.E can be
(i) a point which coincides with a machining starting point M.sub.S [see FIG. 10(a)];
(ii) a point obtained by moving past the machining starting point M.sub.S by a predetermined amount .DELTA..alpha. [see FIG. 10(b)]; or
(iii) a point short of the machining starting point M.sub.S by a predetermined amount .DELTA..alpha. [see FIG. 10(c)].
In FIG. 10, PT represents a wire electrode path, and H denotes a machining starting hole. The wire path patterns in FIGS. 10(a), (b) and (c) are indicated by the solid lines in FIGS. 10(d), (e) and (f), respectively.
In the case of (i), the coordinates of the machining end point M.sub.E can be obtained in a simple manner since the machining starting point M.sub.S and machining end point M.sub.E coincide. In the cases of (ii) and (iii), however, the coordinates of the machining end point must be found by a manual calculation based on using the predetermined amount .DELTA..alpha. and the path data. Calculating the coordinates is very troublesome, especially when the machining end point M.sub.E resides on a circular arc.
Accordingly, an object of the present invention is to provide an NC data creation method for wire-cut electrical discharge machining, in which the coordinates of the machining end points need not be manually calculated and entered each time.